I've seen it happen twice when I immobilized a sorc. They streak immediately after being captured, and at the end of their streak, they are actually immobilized but too far away for it to make much of a difference.
What you are seeing is a timing issue on the server-side. The sorc is probably streaking right as you lay down talons (assuming DK) and the server lets both happen even though only one should. Personally, I think the server should err on the side of defense when actions are that close.